High-surface area co-electrospun TiO₂ nanowires fabricated using shrinkage of polyvinylpyrrolidone for improved photovoltaic performance

Surface-roughened TiO₂ nanowires (NWs) were fabricated using co-electrospinning with different molecular weights of polyvinylpyrrolidone (PVP) polymer: low molecular weight PVP (M_w=360,000 g/mol) for the core region and high molecular weight PVP (M_w=1,300,000 g/mol) for the shell region. Together with the formation mechanism, their surface property, morphology, crystal structure, and photovoltaic performance were studied. The results showed that the surface-roughened TiO₂ NWs had an enhanced specific surface area because of the rough NW surface compared to the pure TiO₂ NWs. As a result, the short-circuit current density (8.94 mA/cm²) of DSSCs fabricated with the surface-roughened TiO₂ NWs is higher than that (5.88 mA/cm²) of the pure TiO₂ NWs. Therefore, the photoconversion efficiency of the surface-roughened TiO₂ NWs exhibited a high value of ~3.63% compared to that of the pure TiO₂ NWs. This phenomenon can be explained by the enhancement of short-circuit current density by an increased dye adsorption; this is because of the increased specific surface area induced by the NW shrinkage due to the different thermal decomposition behavior of PVP depending on the different molecular weights of PVP.